A manifestation of coronary artery disease is the build-up of plaque on the inner walls of the coronary arteries, which causes narrowing or complete closure of these arteries, resulting in insufficient blood flow. This deprives the heart muscle of oxygen and nutrients, leading to ischemia, possible myocardial infarction, and even death. Surgery to alleviate this problem often involves creating an anastomosis between a coronary artery and a graft vessel to restore a blood flow path to essential tissues. An anastomosis is a surgical procedure by which two vascular structures, such as a graft vessel and a coronary artery, are interconnected.
Current methods available for creating an anastomosis include hand suturing the vessels together. Connection of interrupted vessels with stitches has inherent drawbacks. For example, it is difficult to perform and requires great skill and experience on the part of the surgeon due in large part to the extremely small scale of the vessels. For example, the coronary arteries typically have a diameter in the range of between about 1 to 5 mm, and the graft vessels have a diameter on the order of about 1 to 4 mm for an arterial graft such as a mammary artery, or about 4 to 8 mm for a vein graft such as a saphenous vein. Other drawbacks of connection with stitches are the long duration of the operation, during which period in conventional open-heart coronary artery bypass graft (CABG) surgery the heart is arrested and the patient is maintained under cardioplegic arrest and cardiopulmonary bypass. Cardiopulmonary bypass has been shown to be the cause of many of the complications that have been reported in conventional CABG, such as stroke. The period of cardiopulmonary bypass should be minimized, if not avoided altogether, to reduce patient morbidity.
One approach to coronary artery bypass grafting that avoids cardiopulmonary bypass is performing the suturing procedure on a beating heart. At present, however, safe, reproducible, and precise anastomosis between a stenotic coronary artery and a bypass graft vessel presents numerous obstacles including continuous cardiac translational motion which makes meticulous microsurgical placement of graft sutures extremely difficult. The constant translational motion of the heart and bleeding from the opening in the coronary artery hinder precise suture placement in the often tiny coronary vessel.
The above mentioned drawbacks of hand suturing have led to the development of various approaches to stitchless vascular connection or anastomosis which has the advantage of quick and simple execution and undamaged vascular endothelium. Some approaches to stitchless anastomosis used rigid rings prepared from various materials. For example, Geotz et al., INTERNAL MAMMARY-CORONARY ARTERY ANASTOMOSIS--A Nonsuture Method Employing Tantalum Rings, J. Thoracic and Cardiovasc. Surg. Vol. 41 No. 3, 1961, pp. 378-386, discloses a method for joining blood vessels together using polished siliconized tantalum rings which are circumferentially grooved. The free end of the internal mammary is passed through a ring chosen according to the size of the stenotic coronary artery. The free end of the mammary artery is everted over one end of the ring as a cuff and fixed with a silk ligature which is tied around the most proximal of the circular grooves in the ring. The cuffed internal mammary artery is inserted into an incision in the target coronary artery. The ring is fixed in place and sealingly joined to the target coronary artery by tying one or more sutures circumferentially around the target vessel and into one or more circular grooves in the ring. An intimal-to-intimal anastomosis results and dissection of blood between the coronary artery and the cuffed internal mammary artery is largely prevented.
The use of metallic coupling rings is also disclosed in Carter et al., Direct Nonsuture Coronary Artery Anastomosis in the Dog, Annals of Surgery, Volume 148, No. 2, 1958, pp. 212-218 (describing use of rigid polyethylene rings for stitchless vascular connections). Moreover, for example, U.S. Pat. No. 4,624,257 to Berggren et al. describes a device consisting of a pair of rigid rings each having a central opening through which the end of the coronary or graft vessel is drawn and everted over the rings. A set of sharp pins extends outwardly from the face of each ring and pierce through the vessel wall in the everted configuration. The rings are then joined together to align the end of the graft vessel with the opening in the target vessel.
However, no permanently satisfactory results have been reported with the use of rigid rings. A rigid ring presents a foreign body of relatively heavy weight which does not heal well and produces pressure necrosis. Moreover, the use of rigid rings that completely encircle the graft vessel and the arteriotomy creates a severe "compliance mismatch" relative to both the coronary artery and the graft vessel at the anastomosis site which could lead to thrombosis. That is, recent studies suggest that the anastomosis site should not be dramatically different in compliance relative to either the coronary artery or the vascular graft, which is the case when using rigid rings to sealingly join two vessels together.
Another method currently available for stitchless anastomosis involves the use of stapling devices. These instruments are not easily adaptable for use in vascular anastomosis. It is often difficult to manipulate these devices through the vessels without inadvertently piercing a side wall of the vessel. Moreover, as noted above, the scale of the vessels is extremely small, and it is extremely difficult to construct a stapling device that can work reliably on such a small scale to provide a consistent and precise leak-free vascular anastomosis.